Dynamic control for wireless devices

ABSTRACT

A method for determining an attribute of a carrier sense multiple access with collision avoidance (CSMA/CA) scheme, the method may include receiving, by an interface of a wireless communication device, an input signal; calculating, by a processor of the wireless communication device, a strength of the input signal; and determining, by the processor, the attribute of the (CSMA/CA) scheme in response to the strength of the input signal

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/283,319 filing date May 21, 2014 that claims priority from U.S.provisional patent Ser. No. 61/836,681 filing date Jun. 19, 2013, bothapplications being incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to the field of wireless local area networks.

BACKGROUND OF THE INVENTION

In a wireless network that uses carrier sense multiple access withcollision avoidance, CSMA/CA, as its basic access mechanism a receivingstation listens to the wireless medium before transmitting, and if themedium is busy, it will not transmit but will wait until the medium isclear. This is so as to avoid collisions in the medium. An example ofsuch a wireless network is one that is based upon the IEEE 802.11standard, commonly known as Wi-Fi. To meet this requirement a receivingstation commonly has two methods of sensing the medium: physical carriersense and virtual carrier sense. The physical carrier sense senses thatthere is radio frequency activity above a certain threshold whereas thevirtual carrier sense decodes the received transmission and detects avalue that is contained in the transmitted signal that is known in theIEEE 802.11 standard as the network allocation vector, NAV. The NAV is avalue that indicates to all stations that receive the signal the timethat remains before the medium will become free again after thetransmitted packet has ended. In the case of a single packettransmission, the NAV allows time for that packet to be acknowledged.The physical and virtual carrier sense mechanisms in practice exert anindication to the station that informs the station that it shall nottransmit. This indication is generally known as clear channelassessment, CCA. Hence, if CCA is exerted in a station, then thatstation will not transmit. IEEE802.11-2007 and all previous versions,specify the received signal levels for CCA to be exerted for any validsignal and for any radio frequency energy level detected. These levelsare known as the CS/CCA (carrier sense CCA) threshold and ED-CCA (energydetect CCA) threshold respectively. For example, in general, for 20 MHzchannels, any valid signal detected at or greater than −82 dBm shallexert CCA, and any energy level detected at or greater than −62 dBmshall also exert ED-CCA. The figure of −82 dBm is based upon thespecified minimum modulation and coding rate sensitivity. Thesensitivity threshold of a station can also determine the CCA threshold.If the receive sensitivity threshold of a station is higher than theCS/CCA threshold, for example, the effective CS/CCA threshold will bethe receive sensitivity threshold.

A simplified block schematic diagram of the receiver section 10 of astation that uses CSMA/CA is shown in FIG. 1.

The radio frequency signal received at the antenna 11 is amplified byamplifier (such as low noise amplifier LNA) 12 and then converted todigital form by analog to digital converter (ADC) 13. After being mixedby mixer 14 to convert the received frequency to the baseband frequency,the signal is applied to the digital front end block 15. The processescarried out in this digital front end block 15 include amplification bya digital amplifier (digital Amp) 16, applying an automatic gain controlscheme by automatic gain controller (AGC) 18, undergo an input signalattribute measurement such as a received signal strength indicator(RSSI) measurement by RSSI module 19, and signal detected by signaldetector 17. Note that there is a direct relationship between RSSI andthe received signal strength. AGC 18 will measure the radio frequency,RF, energy level detected.

The RSSI indication is effectively a measurement of the received signallevel of a valid received signal. The signal detect block will indicatethat a received signal, greater than the received signal detectthreshold has been received and will indicate that the medium is busy,or that CS/CCA or ED-CCA is exerted, and cause the received signal to beprocessed. Hence, the AGC 18 indicates the general RF energy detected,and the RSSI 19 indicates the received signal strength of a validsignal. The settings of the relevant thresholds are set using registers20. The RSSI value is also written to a register which is then read bythe medium access control, MAC, block 22. The processed signal from thedigital front end 15 is demodulated by demodulator 23 and passed to themedia access control (MAC) module 22.

There are three basic thresholds for the signal detector 17: receivesensitivity threshold, CS/CCA threshold and ED-CCA threshold.

The receive sensitivity threshold sets the level of the minimumsensitivity of the receiver, any signal, valid or not, that is at alevel below this threshold will not be processed in any way, it iseffectively lost or undetected.

The CS/CCA threshold is a value received by the signal detector 17 fromthe MAC module 22 and sets the level at which any valid signal that isreceived above this level will exert CCA and declare the medium busy.

ED-CCA threshold is a value received by the signal detect block from theMAC module 22 and sets the level at which any RF energy that is receivedabove this level will exert ED-CCA and declare the medium busy.

As long as the receive sensitivity threshold is set to a level higherthan the CCA threshold, then an RF signal that is received at less thanthis threshold would not be detected and hence the receive sensitivitythreshold would also set the CCA threshold. For example, if the CS/CCAthreshold is −82 dBm and the receive sensitivity threshold is set to −75dBm, then the effective CS/CCA threshold would also be −75 dBmirrespective if the CS/CCA threshold was set to −82 dBm. Also, if theCS/CCA threshold were set to −82 dBm, the ED-CCA threshold set to −62dBm and the receive sensitivity threshold is set to, say −50 dBm, thenthe effective ED-CCA threshold would be −50 dBm.

Having a fixed CCA threshold can often result in a station beingprevented from transmitting even when, in fact, it could transmitwithout causing any interference to the other station that is the causeof the CCA being exerted. To better explain this situation, fourexamples are given.

Example 1 is shown in FIG. 2. A station, STA A, 30, is located at adistance D from its own access point, AP1, 31 and another station, STAB, 33 in an overlapping network is located at a distance of 4D from AP131 and 2D from STA A, 30.

Indoor RF propagation loss for this type of indoor application can beassumed to be in the order of 10 dB per octave which is a distancefactor of about 35 log(d), where d is the distance. Assume that at AP131 the signal strength from STA A 30 is −50 dBm. Then the signalstrength from STA B 33 which is four times the distance away from AP1 31than STA A 30, and behind a wall 35 that has a penetration loss of 10dB, will be in the order of −80 dBm. Hence, with a difference of 30 dBin the relative signal strengths of STA A 30 and STA B 33, AP1 31 canreceive a transmission from STA A 30 at the same time that STA B 33 istransmitting. The signal to noise plus interference ratio, SNIR, at AP131 is in the order of 30 dB, more than sufficient for good reception.Similarly, in this example, AP2 32 can receive a signal from STA B 33while STA A 30 is transmitting. Note, however, that in this example, STAA 30 will receive a signal from STA B 33 at a level of about −66 dBm;therefore if the common specified value of −82 dBm is used for theCS/CCA threshold, if STA B 33 is transmitting then that signal from STAB 33 will exert CCA in STA A 30 and STA A 30 will not transmit. Thepoint to be noticed is that in this example, both STA A 30 and STA B 33could transmit at the same time and their respective access points, AP131 and AP2 32 would receive their respective signals without problem,but in order to do this, the CS/CCA threshold or receive sensitivitythreshold would need to be set higher, say −60 dBm.

Example 2 is shown in FIG. 3. This example is for an apartment block 40where any particular apartment is surrounded by other apartments oneither side, above and below. The received signal strengths in the homeapartment 41, from each surrounding apartment, can be estimated using anempirical formula for indoor propagation loss. Such a formula is that ofErceg et al, 2004, “TGn Channel Models”, IEEE 802.11-03/940 r4.Calculated results for the received signal strengths in the homeapartment 41 and the surrounding apartments are shown in FIG. 3. In thisparticular case the assumed apartment size is 20 by 35 feet. Note that,in this example, assuming a CS/CCA threshold of −82 dBm, a station inthe selected home apartment 41 is subject to potential interference from32 surrounding apartments.

In the 2.4 GHz band there are only three non-overlapping channels, andin the 5 GHz band there are about 20 channels of 20 MHz bandwidth andonly 10 channels of 40 MHz bandwidth, depending on different areas ofthe world, hence the probability of overlap and interference is high.If, however, the CCA threshold or the receive sensitivity threshold wereset to −50 dBm, then this would result in a station within the selectedhome apartment 41 being subject to possible interference from only 4surrounding apartments, down from 32. Within the home apartment 41 theminimum signal strength is in the order of −38 dBm but note that thehighest signal from any apartment other than the 4 immediatelysurrounding the home apartment, is in the order of at least −60 dBm; aminimum of 22 dB difference. Hence, in this example, if the CS/CCAthreshold or receive sensitivity threshold is set to −50 dBm and thereare at least 5 channels available, then the home apartment 41 couldselect a channel and transmit at the same time as any other network inany other apartment. If all apartments had networks where the CS/CCAthreshold or receive sensitivity threshold was set to −50 dBm, thenbecause the network in each apartment had a maximum of only 4overlapping interfering networks, the channel reuse is significantlyimproved and, for example, each network could operate using anindependent 40 MHz channel.

Example 3 is that of the case of terraced houses as shown in FIG. 4.

In this example the positions of the stations, STA 1, 71, STA 2, 72, STA3, 73 and STA 4, 74, are chosen so as to represent the worst case forinterference to STA 1, 71. The received signal strengths at the variousdevices can be estimated using the Erceg formula for indoor propagationloss. Assuming a penetration loss of 10 dB for the walls, the calculatedresults for received signal strength for the STAs are:

STA 1, 71, STA 2, 72, STA 3, 73 and STA 4, 74 to respective APs −48 dBm

STA 2, 72, to STA 1, 71 −34 dBm

STA 3. 73, to STA 1, 71 −68 dBm

STA 4, 74 to STA 1, 71 −84 dBm

Note that with the default CS/CCA threshold value of −82 dBm, STA 2, 72,and STA3, 73, would both exert CCA on STA 1, 71, if they used the samechannel and that STA 4, 74, may exert CCA at STA 1, 71, periodically.Note that if the CS/CCA threshold of STA 1, 71, were set to −50 dBm, oreven −60 dBm, then transmissions from STA 3, 73, or STA 4, 74, would notcause STA 1, 71 to exert CCA and STA 1, 71, could transmit at the sametime that STA 3, 73, or STA 4, 74, was transmitting. Note also that inthis case, the transmission from STA 3, 73, to AP3, 63, would besuccessful as the SNIR at AP2, 62, would be at least 20 dB. Furthermore,as STA 1, 71, is at the furthest possible distance from its AP, AP1, 61,note that any station located in the same house as STA 3, 73, couldtransmit at the same time as any station in the same house as STA 1, 71,with an SNIR of 20 dB or more and hence have a successful communication,and vice versa. However, if the STAs are using the default CS/CCAthreshold of −82 dBm, this is not the case and only one station couldtransmit at a time. As in the previous examples, raising the CCAthreshold or the receive sensitivity threshold would allow simultaneoustransmissions and increase the potential throughputs of the networks.

Example 4 is shown in FIG. 5 and represents using a 7-cell cluster ofnetworks with an AP situated at the center of each cell.

Two adjoining seven cell structures are shown. Seven different channelfrequencies are used, one for each of the 7 cells in each cluster. Asshown in FIG. 5, the same channel frequency that is used in the cellwhere STA A 91 and AP A 81 are located is also used in the cell whereSTA B 92 and AP B 82 are located. The positions of STA A 91 and STA B 92are chosen to represent a worst case. Assuming that the radius of eachcell is r then the distances between the APs and STAs of interest, usingstandard geometry, are:

Distance STA A 91 to AP A 81=r

Distance AP A 81 to AP B 82=4.77r

Distance STA A 91 to STA B 92=2.64r

Distance STA B 92 to AP A 81=3.61r

Assuming the propagation loss due to distance is 35 log(d), where d isthe distance, and assuming an additional obstruction loss of 3 dB percell wall, then STA A 91 will receive transmissions from STA B 92 at alevel equal to −(35 log(2.64)+9)=−24 dB relative to a signal from AP A81. Also, AP A 81 will receive a signal from STA B 92 at a level of −(35log(3.61)+9)=−29 dB relative to a signal from STA A 91. If we assume acell radius of 40 feet, then the signal strength of the signals betweenSTA A 91 and AP A 81, using the Ecerg formula, is in the order of −50dBm, and similarly the signal strength of the signals between STA B 92and AP B 82, is also in the order of −50 dBm. Hence STA A 91 wouldreceive transmissions from STA B 92 at a signal strength of about−50−24=−74 dBm which is high enough to cause STA A 91 to exert CCA andhence prevent both STA A 91 and STA B 92 from transmitting at the sametime. If STA A 91 could set its CS/CCA threshold or its receivesensitivity higher than −74 dBm, then STA B 92 transmissions would notexert CCA in STA A 91 and STA A 91 could transmit at the same time asSTA B 92 with sufficient SNIR. Similarly if STA B 92 set its CS/CCAthreshold or receive sensitivity threshold higher than −74 dBm, then STAA 91 transmissions would not exert CCA in STA B 92 and STA B 91 couldtransmit at the same time as STA A 91 with sufficient SNIR. Therefore,if the CS/CCA threshold or the receive sensitivity threshold was set at−50 dBm or −60 dBm, and there were at least 7 channels available, then aseven cell cluster network area layout is possible. Using the defaultCS/CCA threshold a seven cell cluster layout is not possible.

In each of these examples it is shown that practical situations existwhere networks on the same channel could be transmitting simultaneouslybut are prevented from doing so because of the default CS/CCA threshold.To overcome this, the CS/CCA threshold or the receive signal thresholdcould simply be set to a higher value but, as will be shown later, thisdoes not result in a network coverage area that accommodates all theSTAs that are within the desired area. An alternative may be to usetransmit power control, TPC. The major problem with TPC is that unlessevery STA in the network and, more importantly, every STA in allsurrounding networks is using TPC, it does not produce the desiredeffect. In addition if one STA or network uses TPC it puts itself at adisadvantage as it effectively can make itself hidden from other STAsand networks and hence experience problem in competing for the medium.Therefore, there is no incentive for a STA or network to use TPC.

SUMMARY OF THE INVENTION

According to an embodiment of the invention there may be provided awireless communication device, a method and a computer readable medium.

There may be provided a method for determining an attribute of a carriersense multiple access with collision avoidance (CSMA/CA) scheme, themethod may include receiving, by an interface of a wirelesscommunication device, an input signal; calculating, by a processor ofthe wireless communication device, a strength of the input signal; anddetermining, by the processor, the attribute of the (CSMA/CA) scheme inresponse to the strength of the input signal.

The input signal may be a management frame that may be transmitted by anaccess point to which the wireless communication device may beassociated.

The input signal may be a beacon frame that may be transmitted by anaccess point to which the wireless communication device may beassociated.

The determining of the attribute of the (CSMA/CA) scheme may beresponsive to the strength of the input signal when the strength of theinput signal does not exceed an upper limit.

The determining of the attribute of the (CSMA/CA) scheme may includesetting a clear channel assessment threshold in relation to the strengthof the input signal.

The method may include setting the clear channel assessment threshold toa level that may be equal to the strength of the input signal minus amargin.

The method may include calculating the strength of the input signal byaveraging strengths of input signals that were calculated at differentpoints in time within a time period.

The method may include counting a number of successive missed beaconframes; defining a limit for a number of successive missed beaconframes; and reducing the attribute of the (CSMA/CA) scheme when thenumber of successive missed beacons exceeds the limit.

The attribute of the (CSMA/CA) scheme may be a receive sensitivitythreshold.

The method may include setting the receive sensitivity threshold to alevel that may be equal to the strength of the input signal minus amargin.

The method of claim may include calculating the strength of the inputsignal by averaging strengths of input signal that were calculated atdifferent points in time within a time period.

The method may include counting a number of successive missed beaconframes; defining a limit for a number of successive missed beaconframes; and reducing the attribute of the (CSMA/CA) scheme when thenumber of successive missed beacons exceeds the limit.

There may be provided a wireless communication device that may includean interface and a processor; wherein the interface may be arranged toreceive an input signal; wherein the processor may be arranged tocalculate a strength of the input signal; and determine the attribute ofthe (CSMA/CA) scheme in response to the strength of the input signal.

The wireless communication device may include a transmitter, wherein thetransmitter may be arranged to transmit output signals according to theattribute of the (CSMA/CA) scheme.

The input signal may be a management frame that may be transmitted by anaccess point to which the wireless communication device may beassociated.

The input signal may be a beacon frame that may be transmitted by anaccess point to which the wireless communication device may beassociated.

The processor may be configured to determine the attribute of the(CSMA/CA) scheme in response to the strength of the input signal whenthe strength of the input signal does not exceed an upper limit.

The processor may be configured to determine the attribute of the(CSMA/CA) scheme by setting a clear channel assessment threshold inrelation to the strength of the input signal.

The processor may be configured to set the clear channel assessmentthreshold to a level that may be equal to the strength of the inputsignal minus a margin.

The wireless communication device of claim wherein the processor may beconfigured to calculate the strength of the input signal by averagingstrengths of input signals that were calculated at different points intime within a time period.

The processor may be configured to count a number of successive missedbeacon frames; define a limit for a number of successive missed beaconframes; and reduce the attribute of the (CSMA/CA) scheme when the numberof successive missed beacons exceeds the limit.

The attribute of the (CSMA/CA) scheme may be a receive sensitivitythreshold.

The processor may be configured to set the receive sensitivity thresholdto a level that may be equal to the strength of the input signal minus amargin.

The processor may be configured to calculate the strength of the inputsignal by averaging strengths of input signal that were calculated atdifferent points in time within a time period.

The processor may be configured to count a number of successive missedbeacon frames; define a limit for a number of successive missed beaconframes; and reduce the attribute of the (CSMA/CA) scheme when the numberof successive missed beacons exceeds the limit.

There may be provided a non-transitory computer readable medium thatstores instructions that once executed cause a wireless communicationdevice to computer to receive an input signal; calculate a strength ofthe input signal; and determine the attribute of the (CSMA/CA) scheme inresponse to the strength of the input signal.

BRIEF DESCRIPTION OF DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 illustrates a prior art wireless receiver;

FIG. 2 illustrates a prior art wireless communication network;

FIG. 3 illustrates attenuations of an apartment building;

FIG. 4 illustrates a prior art network located in a building;

FIG. 5 illustrates a prior art 7-cell cluster of networks with an accesspoint situated at the center of each cell;

FIG. 6 illustrates contention areas of a wireless network using a fixedCCA threshold;

FIG. 7 illustrates contention areas of a wireless network using adynamic CCA threshold according to an embodiment of the invention;

FIG. 8 is a flow chart diagram of a method for a basic derivation of thesetting of the CCA threshold using DSC according to an embodiment of theinvention;

FIG. 9 is a flow chart for a method for derivation of the CCA thresholdvalue according to an embodiment of the invention;

FIG. 10 is a schematic diagram that illustrates effective contentionareas when using DSC with UL set to −30 dBm and M set to 20 dB accordingto an embodiment of the invention;

FIG. 11 is a schematic diagram that illustrates the effective contentionareas when using DSC with UL set to −40 dBm and M set to 20 dB accordingto an embodiment of the invention;

FIG. 12 is a schematic diagram that illustrates the effective contentionareas when using a fixed value for CCA threshold;

FIG. 13 is a schematic diagram showing two seven segment cell clustersaccording to an embodiment of the invention;

FIG. 14 is a schematic diagram of an area that includes a number ofcells according to an embodiment of the invention;

FIG. 15 is a flow chart of a method according to an embodiment of theinvention;

FIG. 16 illustrates a stage of the method of FIG. 15 according to anembodiment of the invention;

FIG. 17 is a flow chart of a method according to an embodiment of theinvention; and

FIG. 18 illustrates a wireless communication device according to anembodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

Because the illustrated embodiments of the present invention may for themost part, be implemented using electronic components and circuits knownto those skilled in the art, details will not be explained in anygreater extent than that considered necessary as illustrated above, forthe understanding and appreciation of the underlying concepts of thepresent invention and in order not to obfuscate or distract from theteachings of the present invention.

Any reference in the specification to a method should be applied mutatismutandis to a system capable of executing the method and should beapplied mutatis mutandis to a non-transitory computer readable mediumthat stores instructions that once executed by a computer result in theexecution of the method.

Any reference in the specification to a system should be applied mutatismutandis to a method that may be executed by the system and should beapplied mutatis mutandis to a non-transitory computer readable mediumthat stores instructions that may be executed by the system.

Any reference in the specification to a non-transitory computer readablemedium should be applied mutatis mutandis to a system capable ofexecuting the instructions stored in the non-transitory computerreadable medium and should be applied mutatis mutandis to method thatmay be executed by a computer that reads the instructions stored in thenon-transitory computer readable medium.

In order to improve the overall throughput and efficiency of wirelessnetworks, a scheme is proposed where either the CCA threshold or thereceive sensitivity of a station is dynamically adjusted such that theeffective CCA threshold meets the prevailing conditions. By so doing,this allows simultaneous transmissions from overlapping networks whichare presently prevented from doing so. This scheme is termed dynamicsensitivity control, DSC.

DSC is a scheme which enables wireless stations to set their receivesensitivity thresholds such that they can receive the wanted signals andreduce the reception of unwanted signals from other interfering devices.In one embodiment, in a wireless network that uses CSMA/CA as the meansto gain access to the medium, for example a Wi-Fi network, the DSC STAcontinuously records the received signal strength of signals, such asthe beacons, from the AP to which it is associated, over a presetperiod. The DSC STA then calculates an average updated value of thereceived signal level. The setting of the receive sensitivity thresholdand hence the effective clear channel assessment, CCA, threshold is thenset at a certain margin below the averaged signal level. This level isupdated at regular intervals. By setting the upper value of the receivesensitivity threshold and the value of the margin, the contention areafor a network can be set and improvements to channel re-use and overallarea data throughputs result. A DSC STA can be used either by itself orin a managed network with DSC where the AP advertises the values for theupper limit and margin and the AP sets its own sensitivity thresholdaccordingly.

There is provided a wireless communication device (such as a stationSTA) that measures the received signal strength of transmissions over aperiod of time. The STA then sets its CCA threshold, either directly orby setting its receive sensitivity threshold, to a value equal to theaverage received signal strength minus a margin. For example, inwireless local area network, WLAN, using CSMA/CA, if the averagereceived signal strength of signals from the access point, AP, to whicha STA is associated, is −40 dBm, and the margin is set to 20 dB, thenthat STA would set its effective CCA threshold to −60 dBm. The value ofthe margin ensures that the level of any interfering signal on the samechannel that does not cause that STA to exert CCA, must be such that theSNIR at that STA will be at least the value of the margin, in thisexample 20 dB. An SNIR of 20 dB would correspond to a signal with 16-QAMmodulation and 3/4 coding, for example. It is desirable that all STAswithin the same network are within the CCA threshold of each other STAin the network so that they will all compete equally for the medium andfor this reason an upper limit is required to set the minimum signalstrength level for the average received signal strength from the AP. Forexample, if the STA is very close to the AP, say about 1 foot, then theaverage received signal strength from the AP would be in the order of−15 dBm. With a margin of 20 dB the receive sensitivity threshold, theeffective CS/CCA threshold and the effective ED-CCA would be set to only−35 dBm. This relatively high CCA threshold level may be such that otherSTAs in the same network, that are further than about 12 feet from theSTA would not exert CCA in the STA that is close to the AP. A range ofonly 12 feet only possibly covers a single room and not a completeapartment or a house. Hence, in this case many other STAs in the samenetwork would be hidden from the STA close to the AP and this wouldresult in unfair contention and the network efficiency and throughputwould suffer. For this reason an upper limit value, UL, for the minimumreceived sensitivity is used and that effectively sets the desired areacoverage of the network. For example, if a UL value of −35 dBm is used,then with a margin of 20 dB the highest possible value for CCA thresholdin the network would be −35−20=−55 dBm. This represents a distance ofabout 50 feet as compared to 12 feet in the case that the upper limit isnot used.

In a network, a station, STA is receiving beacons, other managementframes, control frames and data frames from the access point AP or agroup owner GO in the case of a Wi-Fi Direct network. Management framesinclude probe responses, association responses and authenticationresponses as well as beacons. Control frames include acknowledgments,block acknowledgements, RTS and CTS frames. In the following descriptionan AP is assumed but the same processes described would also apply for aGO. Any or a combination of the beacons, other management frames, actionframes or data frames could be used for the STA to assess the meanreceived signal level of the AP transmissions. In the embodimentdescribed hereunder, the signal strength of the beacons is used. Thebeacons are being received on a regular basis, usually at 100 msintervals, at the same data rate and are transmitted at the sametransmit power. Hence, beacons provide a regular, reliable source ofreceived signals for measurement purposes. It should be noted thatalthough the scheme as described in hereunder dynamically adjusts thereceive sensitivity threshold, a variation would be to dynamicallyadjust the CCA threshold directly. Setting the receive sensitivitythreshold at or above the default CS/CCA threshold effectively sets theCS/CCA threshold to the same level as the receive sensitivity threshold.Similarly setting the receive sensitivity threshold at or above thedefault ED-CCA threshold effectively sets the ED-CCA threshold to thesame level as the receive sensitivity threshold. Conversely, if thereceive sensitivity threshold is set below the default CS/CCA or ED-CCAthresholds, then the default CCA thresholds are unaffected.

The STA records the received signal strength of each of the beacons fromthe AP to which it is associated. In practice the STA will probablyrecord the RSSI value, where RSSI is the received signal strengthindicator. There is a direct relationship between RSSI and the receivedsignal strength. The STA then calculates an average updated value of thereceived signal level over a set period. The STA may use a simpleaverage or a moving average scheme to calculate the average signal levelover a set time period. The received signal strength will vary over timewith movement and as conditions change around the STA. At the end ofeach time period, the receiver sensitivity threshold of the STA is thenset to a value that is at a fixed margin below the average receivedsignal level. This receiver sensitivity threshold value is thereforeupdated at regular intervals. For example, assume that it is desired toupdate the received sensitivity threshold updates at 1 second intervals.At 100 ms intervals the STA would note the received signal strengthmeasurement of the beacon and calculate the running average of thesignal level for a period of one second. Then at one second intervalsthe STA will set or reset its receiver sensitivity threshold value. Bysetting its receive sensitivity threshold, if this threshold is equal orabove the CCA threshold, the STA is also effectively setting theeffective CCA threshold level.

This process is termed dynamic sensitivity control, DSC. A station usingDSC is termed a DSC STA.

There are two basic settings for DSC: the upper limit, UL, and margin,M. In general the DSC STA measures the average signal strength of thereceived beacon, R dBm, and then subtracts the margin M dB to arrive atthe value for the receiver signal strength threshold. For example, ifthe average signal strength, R, of the beacon is −45 dBm and the margin,M, is set to 20 dB, the receive sensitivity threshold of the DSC STA isset to R−M=−45−20=−65 dBm. Hence, in this case, no received signal witha signal strength of less than −65 dBm will be recognized by thatstation. Assuming an internal wall loss of 3 dB and walls spaced every20 feet, this particular sensitivity would correspond to a distance inthe order of 70 feet for signals from other stations that would bereceived by the DSC STA and would exert CCA at the DSC STA. If the DSCSTA is very close to its AP, say about 1 foot distance, then thereceived beacon signal strength would be in the order of −15 dBm. Inthis case the receive sensitivity threshold could be set to −35 dBm,which represents a much more limited range of about 10 to 15 feet andother stations in the same network that are further away than 15 feetfrom the DSC STA would not be received by the DSC STA and hence behidden to the DSC STA. The network efficiency would then suffer as thecontention for the medium is then unfair. The upper limit, UL, is set torepresent the maximum value for the received signal strength of thebeacon that can be set as the received signal strength and thuseffectively sets the minimum receiver sensitivity threshold as UL−M. Forexample, if the upper limit, UL, is set to −30 dBm and the margin, M,set to 20 dB, then the minimum value for the receive sensitivitythreshold is UL−M=−30−20=−50 dBm, a range of about 40 feet. Setting theupper limit and margin values it is possible to set the effectivenetwork coverage area wherein all stations would contend.

If a fixed CCA threshold is used, then the result is that the coveragearea of a network has large areas where other STAs are effectivelyhidden with the result that the contention in network does not cover allthe stations in the network and the basic CSMA/CA scheme breaks down.This problem is presented in FIG. 6.

FIG. 6 represents a network of at least 5 STAs, 115, 120, 125, 127, 130.As shown in FIG. 5, a fixed value for CCA threshold is used, and thecontention area around each STA in the network is a circle and eachcircle around each STA 115, 120, 125, 127, 130 is of the same radius. Inthis example, the setting of the CCA threshold is such that the radiusof the contention area circle 105 for STA 5 130 is just within the rangeof STA 1, 115, which is located close to the AP 110, such that STA 5,130, will exert CCA in STA 1, 115, and vice versa. If the STAs 115, 120,125, 127, 130 are equally spaced 10 feet apart and the CS/CCA thresholdis fixed and set to −50 dBm, the contention area circles 101, 102, 103,104, 105 as shown in FIG. 6 result. In this case, any other STAs in thenetwork that are located in the area outside of the circle 105 that iscentered on STA 5, 130 namely all the area 195 that is shaded in FIG. 6,will be hidden from STA 5, 130, but not from STA 1, 115, and hence thecontention is now unfair. In this particular case, STA 1, 115, wouldsuffer as it will need to defer to transmissions from STA 5, 130, andany other STA within the shaded area 195, which will curtail its abilityto transmit, and, in addition, transmissions from STA 5, 130, and anySTA within the shaded area 195 are prone to clash at the AP 110 and notbe successful. Similarly for STA 2, 120, STA 3,125, and STA 4,127, shownin FIG. 6, the size of the areas 192, 193, 194 where hidden STAs can belocated varies according to the distance of each STA, 120, 125, 127 fromSTA 1, 115, respectively. The result is that the use of a fixed valuefor CCA threshold, especially when the value is to be set at arelatively high value compared to the default setting, can result inmany hidden STAs within a network which results in inefficiency.

FIG. 7 shows a similar network to that shown in FIG. 6 but in this casedynamic sensitivity control DSC is used and the STAs, 215, 220, 225,230, 235 are DSC STAs. In the example network shown in FIG. 7, the DSCsetting for upper limit, UL, is −30 dBm and the setting of the margin,M, is 20 dB.

The five DSC STAs, 215, 220, 225, 230, and 235 are equally spaced at 10feet spacing from the AP 210; STA 1, 215, is 10 feet distance from theAP 210 and STA 5, 235, is 50 feet away from the AP 210. The averagesignal strength of beacons or signals from the AP 210 would be in theorder of −28 dBm at STA 1, 215. As the upper limit is set to −30 dBm andthe margin to 20 dB, the effective CCA threshold for STA 1, 215, will beset to −50 dBm and this corresponds to a circle 201 centered on STA 1,215, with a radius of 40 feet within which any other STA can exert CCAon STA 1, 215. STA 5, 235 is the furthest from the AP 210 at a distanceof 50 feet. To estimate ranges the Ecerg formula is used together withan assumption of an obstruction loss of 3 dB every 20 feet. This 3 dBloss would be representative of an internal wall. Hence STA 5, 235,would receive beacons or signals from the AP with a signal strength ofabout −60 dBm. Hence STA 5, 235, will set its receive sensitivitythreshold and its effective CS/CCA threshold to −80 dBm. The contentionrange therefore for STA 5, 235, corresponds to the circle 205 centeredon STA 5, 235, with a radius of about 95 feet within which any other STAwill exert CCA on STA 5, 235. Note that the contention range circle 205for STA 5, 235, fully encloses the contention range circle 201 for STA1, 215. Similarly, for STA 2, 220, STA 3, 225, and STA 4, 230, theirrespective contention range circles, 202, 203 and 204 respectively, allenclose that of STA 1, 201. Hence, by setting the upper limit to −30 dBand the margin to 20 dB, the network area is set such that all STAswithin the area 201 as shown for STA 1, 215, will all contend correctlyfor the medium. It should also be noted that the AP 210 may also set itsown CCA threshold to be compatible with that of the STAs that areassociated to it. In addition the AP 210 may also provide the values forUL and M that all STA that are associated to it, shall use. This couldbe carried out using an information element in the beacon and proberesponses.

The value used by a DSC STA for the margin needs to be sufficientlylarge so as to provide adequate SNIR. If two DSC STAs or if a DSC STAand a legacy STA are transmitting at the same time, then by definition,the minimum SNIR for each STA will be equal to the value of the margin,M. Examples of the required SNIR for common modulations that provide ahigh data rate are: 30 dB for 256-QAM with 3/4 coding, 25 dB for 64-QAMmodulation with 3/4 coding rate, 22 dB for 64-QAM modulation with 2/3coding rate, 19 for 16-QAM modulation with 3/4 coding rate. The margin,M, represents the absolute minimum SNIR that would be expected. Inaddition, the margin needs to be large enough to account for suddenchanges in the received signal level. If the DSC STA moves behind awall, for example, it should not lose the wanted signal that is used toset the DSC threshold. Therefore the margin should be larger than anexpected sudden decrease due to such a situation. The example used of 20dB should be generally sufficient assuming that with the distribution ofSTAs in an interfering network, the SNIR could be reasonably expected tobe generally greater than the margin M. which represents the absoluteminimum value. However, the value of 20 dB is simply an example and doesnot imply a fixed value. The upper limit, UL, and margin, M, can be setto suit the application, desired network coverage and desired trafficdata rates.

An AP may advertise the values for upper limit and margin that are to beused by DSC STAs associated to that AP and the AP may then set its ownCCA thresholds to be compatible with the DSC STA settings. This abilityhas particular value in enterprise networks and hotspots. In addition,and AP could advertise that the use of DSC is not allowed. This may havevalue when an AP desires that the network area coverage is as large aspossible. The CCA values for M and UL as well as the command that DSC isnot allowed could be advertised in one or more information elements thatthe AP could include in beacons and probe responses.

It should be noted that a station using the proposed scheme, a DSC STA,does not, in general, have an adverse effect on other legacy stations inthe other networks that do not use the scheme. For example, if a legacystation is located in an overlapping network, if that legacy station istransmitting and the DSC STA also starts to transmit, there is no effecton the legacy STA which will complete its transmission. The DSC marginis such that the SNIR at each STA is sufficient for both transmissionsto be successful. In the case that the DSC STA is already transmittingwhen a legacy STA wishes to transmit, the DSC STA will exert CCA at thelegacy STA, and the legacy STA will need to wait until the DSC STA hascompleted its transmission as is the case if the DSC STA were a legacySTA. Hence, in this latter case there is no difference to the legacySTA. In fact in simulations it can be shown that in general there is anoverall advantage to the legacy STA, and the overlapping legacy network,as the simultaneous transmissions by the DSC STA reduce the contentionwait times at the legacy STA which would normally have to wait for theentire duration of each transmission of an overlapping STA.

Dynamic Sensitivity Control (DSC) enables an IEEE 802.11 station (STA)to dynamically set its CCA threshold either directly or by setting thereceiver sensitivity threshold. A STA using DSC is referred to as a DSCSTA. The network controller is an access point (AP) in the case of aninfrastructure network, or a group owner (GO) in the case of a Wi-FiDirect network.

FIG. 8 is a flow chart diagram that shows an embodiment for the basicderivation of the setting of the CCA threshold using dynamic signalstrength, DSC. At step 310 a timer is started. At step 320 the DSC STArecords the received signal level of a signal from the AP to which it isassociated. In practice the STA will probably record the RSSI value,where RSSI is the received signal strength indicator. Any signal orcombination of signals from the AP may be used: management, control ordata frames. At step 330 the received signal level is checked against anupper limit value. If the received signal level from step 320 is higherthan the upper limit value, then in step 340 the signal level recordedin step 320 is replaced with the upper limit value. At step 350, arunning average of the recorded received signal levels from step 340 orthe substituted upper limit values from step 340, is calculated. Anyaveraging calculation may be used in step 350 including but not limitedto a simple average or a moving average scheme. At step 360 the elapsedtime since step 310 is checked. If the elapsed time is greater than anupdate period, then the average signal level from step 350 is converted,in step 370, to determine the setting of the CCA threshold. The CCAthreshold is set to a value that is equal to the average received signallevel from step 350, minus a preset margin. The CCA threshold value maybe directly set as a result of this calculation in step 370, oralternatively the receive sensitivity threshold value for the DSC STAmay be set, which effectively sets the CCA threshold to the same value.

FIG. 9 is a flow chart for the derivation of the CCA threshold valuewhich corresponds to one detailed embodiment of the DSC scheme. In step400 the routine is first initialized as follows:

BeaconCount, the number of consecutive missed beacons, is preset tozero.

BeaconCountLimit, the limit of consecutive missed beacons, is set to apreset value.

An example default value is 5.

UpdatePeriod, the period over which the received signals are averaged,is set to a preset value. An example default value is 1 second.

UpperLimit, UL, the maximum value of received signal strength to beused, is set to a preset value. The equivalent value for RSSI may beused. An example default value is −30 dBm.

RSSI_Decrement, the value, in dBs, that the existing average RSSI orreceived signal strength value is decreased by if the BeaconCountLimitis exceeded. An example default value is 6 dB.

Margin, the value, in dBs, that is subtracted from the average RSSIreceived signal strength value in order to set the received sensitivitythreshold or CCA threshold. An example default value is 20 dB.

Min_RX_Sensitivity, the minimum value for receiver sensitivitythreshold, is set to the value that corresponds to the RX sensitivitythreshold of the STA if DSC was not in use. This value is governed bythe minimum supported modulation rate and the noise figure of thedevice. A typical value would be −91 dBm.

In step 402 the time is set to zero. In step 405 the DSC STA waits for abeacon from the AP to which it is associated. Any transmission from theAP may be used but as the beacons are at a regular rate and are alwaystransmitted at the same power level, they provide a convenient set ofsignals to monitor. Step 410 checks that a beacon is received. Asbeacons are transmitted at a near constant rate, it is straightforwardto determine if a beacon has been missed. If it is determined that thebeacon is missed, then in step 460, the BeaconCount is incremented. Instep 465 the BeaconCount value from step 460 is checked against theBeaconCountLimit preset value from step 400. If the BeaconCount valuedoes not exceed the BeaconCountLimit value, then the flow returns tostep 405 to await the next beacon. If at step 410 the beacon is receivedthen in step 415 the value of BeaconCount, the number of consecutivemissed beacons, is set or reset to zero and the value of the receivedsignal strength or RSSI of the beacon is recorded in step 420. In step425 the value of the recorded signal strength, RSSI, from step 420 ischecked against the UpperLimit preset value from step 400. If the RSSIreading from step 420 exceeds the UpperLimit from step 400, then in step430 the recorded RSSI value from step 420 is replaced by the UpperLimitvalue. The input to step 435 is therefore either the recorded RSSI valuefrom step 420, via step 425, or the UpperLimit value from step 430. Instep 435 the average RSSI value, AverageRSSI, is calculated. Thisaveraging of the received signal strengths may be determined by anyaveraging scheme or indeed by simply taking the latest vale. Theaveraging, if used could be either a simple running average or a movingaverage. In step 440 the elapsed time since the time was set to zeroeither in step 402 or step 475 is checked. If the time has not exceededthe UpdatePeriod preset value from step 400, then the flow is returnedto step 405 to await the next beacon reception. If the time has exceededthe UpdatePeriod preset value from step 400, then in step 445 the latestAverageRSSI value from step 440 is converted to received signalstrength. This conversion in step 445 will be implementation dependentas the actual conversion from RSSI value to equivalent signal strengthvalue may differ for different devices and different manufacturers.Suffice it to say, that the output of step 445 is a signal level valuethat represents the average signal strength of the received beaconsduring a time period of UpdatePeriod as set in step 400. In step 450,the value of the Margin, preset in step 400, is deducted from theaverage signal strength of the received beacons derived during thelatest time period of UpdatePeriod, in order to produce a value forreceive sensitivity, RX_Sensitivity. In step 455 the latest value forRX_Sensitivity is checked against the value of Min_RX_sensitivity whichwas preset in step 400. If the value of RX_Sensitivity exceedsMin_RX_sensitivity then the time is reset to zero in step 475 and theflow returns to step 405 to await the next beacon reception. If thevalue of RX_Sensitivity is less than Min_RX_sensitivity then value ofRX_Sensitivity is set to be equal to Min_RX_sensitivity. The time isthen reset to zero in step 475 and the flow returns to step 405 to awaitthe next beacon reception. In order to account for missed beacons, if atstep 465 the BeaconCount exceeds the BeaconCountLimit, preset in step400, then in step 470 the existing value for AverageRSSI, as determinedfrom a previous step 435, is decremented by a value equal toRSSI_Decrement. RSSI_Decrement is a value preset in step 400. This newvalue is then applied to step 445 so that a new RX_Sensitivity thresholdat step 450 is derived immediately.

The normal flow is that the DSC STA receives Beacon in step 410 andrecords the corresponding RSSI value in step 420. It is then checked, instep 425, if this RSSI value represents a value higher than the UpperLimit the value is recorded as the RSSI equivalent to the Upper Limit.The DSC STA then waits for the next Beacon. Over a period set byUpdatePeriod, the AverageRSSI can be calculated using a variety ofaveraging methods. An example calculation of the AverageRSSI using amoving average is:

AverageRSSI=[RSSI(latest)−RSSI(previous)]/3+RSSI(previous)

The result of such a moving average calculation is that the average RSSIvalue is more influenced by the latest reading than previous ones. Asimple average may be used or the latest value could be used and noaveraging carried out.

Once the UpdatePeriod has expired, in step 440, the AverageRSSI value isconverted to received signal strength in step 445. The correspondingRX_Sensitivity Threshold is then calculated in step 450 by effectivelysubtracting the Margin value from the average value from step 445, andthen checking, in step 455 that it is not less than the minimumRX_Sensitivity. The routine is then repeated for the next UpdatePeriod.

The routine accounts for missed beacons in steps 410, 460, 465 and 470.It is relatively common to miss a certain number of beacons especiallyif the DSC STA is in power save mode. If in a power save mode, the DSCSTA may deliberately sleep through a number of beacons, or it may miss abeacon due to an error in timing, and hence the beacon period used instep 405 and the UpdatePeriod used in step 440 may need to be adjustedto account for this. Beacons could also be missed if the DSC STAsuddenly experiences an increase in propagation loss, such as moving tothe other side of a brick wall. If an expected Beacon is missed in step410, then the BeaconCount is incremented in step 460. The BeaconCount isincremented for each successive beacon loss but reset to zero in step415 if a beacon is received. If the BeaconCount exceeds theBeaconCountLimit, as checked in step 465, then the AverageRSSI value isinstantly decremented by the value of RSSI_Decrement in step 470. Thisinstantly increases the sensitivity of the DSC STA, via steps 445, 450,455 and 457 to counter the perceived drop in signal strength of thereceived beacon. RX_Sensitivity will swiftly drop to the minimum value,Min_RX_Sensitivity, if successive beacons are still missed. Otherroutines that are apart from DSC take place if no Beacons are receivedby a STA for a certain period.

In the embodiment described in FIG. 9, beacons are used to calculate thereceived signal strength. Beacons provide a regular, known signal butany received signal from the AP, or indeed other STAs in the network,could be used to determine the CCA threshold value. Sampling andaveraging the received signal strength over a set period, UpdatePeriod,is used as indoor radio propagation losses can vary significantly withsmall changes in time and position.

Together, the preset values for Upper Limit and the Margin set theminimum value for the RX_Sensitivity Threshold and sets the effectivearea within which all DSC STAs in the network will contend in the normalmanner. This area is referred to as the contention area.

If the Margin is set to M dB, then the DSC STA will receive signals froma STA that is outside the contention area at a level that is at least MdB less than the DSC STA receives signals from its AP. It is desirablethat the STA communicate with the AP at the highest practical data rateand to do this the ratio between the wanted and unwanted signals, theSNIR, should be a value that corresponds to the required SNIR formodulated signals of interest. The Margin represents the minimum valuefor SNIR caused by interfering STAs. Hence, by setting the Margin to 20dB, for example, the SNIR would be effectively set to ensure that wantedsignals with modulation 16-QAM and 3/4 coding would be received. TheRX_Sensitivity Threshold is updated every UpdatePeriod and therefore theMargin value sets a limit to the variation in signal strength for theDSC STA within the update period. Hence the Margin needs to be largeenough to cater for any sudden changes in signal strength that may beexperienced such as, for example, moving behind a wall or going outsidea building.

FIG. 10 is a schematic diagram that illustrates the effective contentionareas when using DSC with Upper Limit, UL, set to −30 dBm and Margin, M,set to 20 dB. The Ecerg propagation formula is used to estimate rangestogether with an assumption of an obstruction loss of 3 dB every 20 feetof distance. This 3 dB obstruction loss is representative of an internalwall every 20 feet. STA 1, 215, is located 10 feet away from the AP 210.At this range the received signal strength at STA 1, 215, of a beaconfrom the AP 210 is in the order of −28 dBm. Hence the RX_SensitivityThreshold for STA 1, 215, would be set UL minus M, which would be −50dBm, in this example. For indoor propagation, the equivalent range for−50 dBm signal strength is about 40 feet. The area 301 shows theeffective contention area for STA 1, 215. All STAs within this area 301would contend. Note that this 40 feet radius area 301 would generally besufficient to cover an apartment or small house. STA 2, 220 is located20 feet from the AP 210. In this case the received signal strength atSTA 2, 220, of a beacon from the AP 210 is in the order of −40 dBm.Hence the RX_Sensitivity Threshold for STA 2, 220, would be set to the−40−20=−60 dBm resulting in the contention area 302, a circle of 50 feetradius. Similarly, STA 3, 225 is at range 30 feet from AP 210 and STA 4,230 is located 40 feet away from AP 210. The received signal strengthsof beacons from AP 210 for STA 3, 225, and STA 4, 230 are about −50 dBmand −53 dBm, which result in values for RX_Sensitivity Thresholds of −70dBm and −73 dBm respectively. The resulting contention areas, 303 and304, are shown as circles of radius 75 feet, and 80 feet respectively.Note that as a STA moves further away from the AP 210 the contentionarea increases but that area always includes the area for the STA thatis closest, STA 1, 215, in this case. As the contention area 301 for STA1, 215, is set by the value of UL minus M, this represents the smallestcontention area that is possible in this network. Hence, contentionareas 302, 303 and 304 all include area 301. Therefore, if the requiredrange of the network in this example was 40 feet, then all STAs withinthat network will contend normally.

FIG. 11 is a schematic diagram that illustrates the effective contentionareas when using DSC with UL set to −40 dBm and M set to 20 dB. TheEcerg propagation formula is used to estimate ranges together with anassumption of an obstruction loss of 3 dB every 20 feet of distance.This 3 dB obstruction loss is representative of an internal wall every20 feet. STA 1, 215, is located 10 feet away from the AP 210. At thisrange the received signal strength at STA 1, 215, of a beacon from theAP 210 is in the order of −28 dBm. Hence the RX_Sensitivity Thresholdfor STA 1, 215, would be set to the UL minus M which would be −60 dBm.For indoor propagation, the equivalent range for −60 dBm signal strengthis about 60 feet. The area 401 shows the effective contention area forSTA 1, 215. All STAs within this area 401 would contend using thestandard routines defined in IEEE 802.11. STA 2, 220 is located 20 feetfrom the AP 210. In this case the received signal strength at STA 2,220, of a beacon from the AP 210 is in the order of −40 dBm. Hence theRX_Sensitivity Threshold for STA 2, 220, would be set again to the−40−20=−60 dBm resulting in the contention area 402, a circle of 60 feetradius centered on STA 2, 220. STA 3, 225 is at range 30 feet from AP210 and STA 4, 230 is located 40 feet away from AP 210. The receivedsignal strengths of beacons from AP 210 for STA 3, 225, and STA 4, 230are about −50 dBm and −53 dBm, which result in values for RX_SensitivityThresholds of −70 dBm and −73 dBm respectively. The resulting contentionareas, 403 and 404, are shown as circles of radius 75 feet, and 80 feetrespectively. In this example, as shown in FIG. 11, by using a highervalue for the upper limit, the network coverage area, as represented bythe common overlapping area, is increased from that in FIG. 10.

FIG. 12 is a schematic diagram that illustrates the effective contentionareas when using a fixed value for CS/CCA threshold. In this example, afixed CS/CCA threshold of −50 dBm is used so that the contention areasin FIG. 12 can be directly compared to those in FIG. 10. STA 1, 115, islocated 10 feet away from the AP 110. The CS/CCA threshold is fixed at−50 dBm. For indoor propagation, the equivalent range for −50 dBm signalstrength is about 40 feet. The area 101 shows the effective contentionarea for STA 1, 115. All STAs within this area 101 would contend usingthe standard routines defined in IEEE 802.11. STA 2, 120 is located 20feet from the AP 110. Again the CS/CCA threshold is set at −50 dBmresulting in the contention area 102, also a circle of 40 feet radius,but this circle is centered on STA 2, 120. Similarly, STA 3, 125 is atrange 30 feet from AP 110 and STA 4, 130 is located 40 feet away from AP110. The CS/CCA threshold is fixed at −50 dBm for each STA hence theresulting contention areas, 103 and 104, are shown as circles of radius40 feet, centered on STA 3, 125 and STA 4, 130 respectively. STA 5, 135is located at about 20 feet distance from AP 110 but on the oppositeside to STA 1, 115. Note that STA 5, 135 does not lie within the areasof contention, 102, 103, and 104, for STA 2, 120, STA 3, 125, and STA 4,130 respectively. Hence, STA 5, 135, will be hidden from STA 2, 120, STA3, 125 and STA 4, 130. In this case the contention within this networkwould be severely impaired. FIG. 12 demonstrates that using a fixedhigher level value than the default value for CS/CCA threshold does notprovide the network area coverage to allow contention to take place. Incontrast, FIG. 11 demonstrates that deriving the CS/CCA threshold usingreceived signal strength together with an upper limit and margin, doesprovide network coverage.

FIG. 13 is a schematic diagram showing two seven segment cell clusters,500 and 550. Area 500 consists of seven cells, 501, 502, 503, 504, 505,506 and 507. Area 550 consists of seven cells, 551, 552, 553, 554, 555,556 and 557. At the center of cell 507 is located AP A, 510. At the edgeof cell 510 is located STA B, 520. Similarly, in cell 557, AP B, 560 islocated at the center and STA B, 570 is located at the edge of cell 570.STA A, 520 and STA B, 570 are located so as to be as close to each otheras possible while remaining in their respective cells, 507 and 557. APC, 580 is located at the center of cell 553. Assuming that the radius ofeach cell is r, then using standard geometry the distance between STA A,520 and STA B, 570 is 2.64r. The distance between AP A, 510, and STA A,520 is r. Assuming propagation loss due to distance as 35 log(d), whered is the distance, and assuming an additional obstruction loss of 3 dBper cell wall, then STA A, 520 will receive transmissions from STA B,570 at a level equal to −(35 log(2.64)+9)=−24 dB relative to a signalfrom AP A, 510. Similarly, STA B, 570 will receive transmissions fromSTA A, 520 at a level −24 dB relative to the signal received from AP B,560. Hence, if DSC is used with a margin of 20 dB, STA A, 520 and STA B,570 will not exert CCA on each other and will be able to transmitsimultaneously. For example, assume that the cell radius r is 40 feet.STA A, 520 is at a distance of 40 feet from AP A, 510 and hence, usingthe Ecerg formula for radio propagation, STA A, 520 will receive signalsfrom AP A, 510 at a signal level of about −50 dBm. STA A, 520 is at adistance of 106 feet from STA B, 570 and hence will receive signals fromSTA B, 570 at a signal strength of about −75 dBm, assuming an additionalobstruction loss of 3 dB per cell wall. Using a DSC scheme with amargin, M, of 20 dB, the receive sensitivity threshold and the effectiveCS/CCA threshold for STA A, 520 will be −70 dBm. Hence, any transmissionfrom any STA that is within cell 557 will not exert CCA on any STA thatis within cell 507. Therefore, if there are at least seven channelsavailable, using DSC, a seven cell cluster area coverage scheme can beconfigured. Note, however, that using the default value for CS/CCAthreshold of −82 dBm, using the same channel for the networks in cells507 and 557 would mean that the two networks would overlap and have toshare and contend. The distance between AP C, 580 and AP A, 510 is 240feet. Transmissions from AP A, 510 will be received by AP C, 580 at asignal strength of about −81 dBm which means that if using the defaultvalue for CS/CCA threshold of −82 dBm, cells 507 and 553 would overlapand contend.

FIG. 14 is a schematic diagram of an area 600 which is comprised of anumber of cells. Area 610 comprises seven cells 611-617 and area 620comprises cells 611-617 and cells 621-650, a total of 37 cells. Area 610represents a seven segment cell cluster.

As was shown in FIG. 13, when using the DSC scheme with a margin, M, of20 dB, it is possible to configure a seven cell cluster pattern usingseven channels. Hence, in the 37 cells represented by area 620, withseven or more available channels, it is possible that every cell can bea separate network that does not overlap or share with any other networkin any other cell.

If the default value for CCA threshold is used, then every other cellwithin the area 620 would overlap and contend with cell 617. Hence, theresult is that using DSC there are 37 separate networks, whereas withthe default CS/CCA threshold there are 37 overlapping networks to cell617. To estimate the capacity improvement the following simplifiedcalculation is given. Assume that the maximum throughput in each cellnetwork is T Mbps.

The total throughput capacity using DSC is simply 37×T Mbps as each cellhas its own channel, one chosen from a pool of 7 channels. In the casewhere default CS/CCA threshold is used, it would be possible to use 7APs in the center of cell 617, but the complete 37 cells area iseffectively one network, so hence the maximum throughput would be 7×TMbps. Therefore using DSC increases the total area throughput of area620 by a factor of at least 37/7=5.29. In fact, it can be shown that duethe fact that in area 620, using the fixed CS/CCA threshold of −82 dBm,there are many hidden cells, the improvement in total throughput byusing DSC is higher and at least 8 times. For example, when using thefixed default CS/CCA, the STAs in cells 621, 622, 623, 626, 627, 638,639, 640, 641, 642, 643, 644, 645, 646, 647, 648, 649, and 650, wouldall be hidden from the STAs in cell 632; a total of 18 out of the 37cells. Similarly, for every cell there will be hidden cells, and theoverall result is that the efficiency of the complete 37 cell network isimpaired.

As shown in FIG. 13 and FIG. 14 if DSC is adopted, the overallthroughput for a particular area can be significantly improved becausethe re-use pattern of channels is improved and more simultaneoustransmissions can take place within the total area.

The AP can set the Upper Limit, U L, and Margin, M, parameters byadvertising them in beacons and probe responses using an informationelement and by so doing set the effective operating area of its network,as was shown in FIG. 10 and FIG. 11. Also the AP can set the CCAthresholds for itself. A variety of methods could be used for the AP todetermine these values, either by pre-set or by a learning process. Forexample an AP could discover the channel and overlapping situation bymonitoring the beacons and traffic from surrounding networks. Thisprocess could be dynamic with subsequent scans of the medium. In generalthe AP setting for the CCA threshold would be set in relation with thevalue (UL−M), where UL and M are the values that the AP might advertise.

FIG. 15 illustrates method 800 according to an embodiment of theinvention. FIG. 16 illustrates stage 850 of method 800 according to anembodiment of the invention.

Method 800 may start by stage 810 of receiving input signals. Theseinput signals are received by a wireless communication device (such as astation) and were transmitted over a wireless network. They may betransmitted by an access point associated with a wireless communicationdevice or by another device (other station, other access point).

Stage 810 may be followed by stage 820 of calculating an input signal'sattribute.

The calculating of the input signal's attribute may be responsive to allor some of the input signals received by the wireless communicationdevice, to all or some of the input signals received from an accesspoint associated with the wireless communication device, to some or allinput signals received from an entity that differs from the access pointassociated with the wireless communication device, to all or some of theinput signals included in data frames, to all or some of the inputsignals included in beacon frames, to all or some of the input signalsincluded in probe responses, to all or some of the input signalsincluded in management frames, to all or some of the input signalsincluded in input signals that are included in frames of predeterminedpower and timing, to all or some of the input signals included in one ormore time windows and the like.

The input signal's attribute may represent at least one of a strengthand power of the input signals.

The input signal's attribute may represent at a statistical functionapplied on values of input signals over a time period.

Stage 820 may include:

-   -   a. Stage 821 of receiving at least one threshold out of a        predetermined strength threshold and a predetermined power        threshold. This stage may include searching the at least one        threshold in any frame received by the wireless communication        device, in some or any frame received from an access point        associated with the wireless communication device, in some or        any frame received from an entity that differs from the access        point associated with the wireless communication device, in some        or any data frame, in some or any beacon frame, in some or any        probe responses, in some or any management frames, in some or        any frames of predetermined power and timing, in some or any        frames received in one or more time windows and the like.    -   b. Stage 822 of calculating the input signals attribute by        ignoring input signal having strength that exceed the        predetermined strength threshold and/or have a power that exceed        the predefined power threshold.

Stage 820 may be followed by stage 830 of determining an attribute of acollision avoidance scheme in response to the input signals attribute.

The attribute of the collision avoidance scheme may be a clear channelassessment threshold.

Stage 830 may include at least one of the following stages:

-   -   a. Stage 831 of determining the clear channel assessment        threshold in response to the input signals attribute.    -   b. Stage 832 of determining the clear channel assessment        threshold such as not to exceed a clear channel assessment        threshold upper limit.    -   c. The clear channel assessment threshold upper limit may be        fixed, may vary over time, may be determined by the wireless        communication device, by an associated access point and the        like. Stage 830 may include stage 833 of calculating or        receiving the clear channel assessment threshold upper limit.        Stage 833 may include searching the clear channel assessment        threshold upper limit in frames from an access point that is        associated with the wireless communication device. These frames        may be beacon frames, management frames and/or probe responses.    -   d. Stage 834 of setting a value of a sensitivity threshold,        wherein a value of the attribute of the collision avoidance        scheme is responsive to the value of the sensitivity threshold.    -   e. Stage 835 of receiving or calculating margin between the        input signals attribute and the attribute of the collision        avoidance scheme. If the margin is received then stage 835 may        include searching the margin in frames from an access point that        is associated with the wireless communication device. These        frames may be beacon frames, management frames and/or probe        responses.

Stage 830 may be followed by stages 840, 850 and 810. Jumping from stage840 to stage 810 facilitates a repetition of stages 810-830 and providesa dynamic process for determining the attribute of the collisionavoidance scheme.

Stage 840 may include applying a collision avoidance scheme. This mayinclude transmitting output signals according to the collision avoidancescheme.

The repetition of stages 810-840 may result in calculating the clearchannel assessment threshold upper limit at different points of time.

Stage 850 may include monitoring events and responding to the events.

Stage 850 may include at least one out of the following stages, allillustrated in FIG. 16:

-   -   a. Stage 851 of monitoring a lack of reception of input frames        that were expected to be received by the wireless communication        device. The input frames that were expected to be received by        the wireless communication device may be beacon frames.    -   b. Stage 852 of updating the attribute of the collision        avoidance scheme in response to the lack of reception of input        frames that were expected to be received by the wireless        communication device. The input frames that were expected to be        received by the wireless communication device may be beacon        frames.    -   c. Stage 853 of reducing the receive sensitivity threshold and        possibly the effective clear channel assessment threshold, if        the receive sensitivity threshold is still higher than the clear        channel assessment threshold, upon a lack of reception of a        predetermined number of successive beacon frames that were        expected to be received by the wireless communication device.    -   d. Stage 854 of reducing the receive sensitivity threshold and        possibly the effective clear channel assessment threshold, if        the receive sensitivity threshold is still higher than the clear        channel assessment threshold, upon a predefined relationship        between beacon frames that were received by the wireless        communication device and beacon frames that were expected to be        received by the wireless communication device but were not        received by the wireless communication device.    -   e. Stage 855 of reducing, by a certain amount, the receive        sensitivity threshold and possibly the effective clear channel        assessment threshold, if the receive sensitivity threshold is        still higher than the clear channel assessment threshold, upon a        lack of reception of at least one input frame that was expected        to be received by the wireless communication device; wherein the        certain amount is fixed.    -   f. Stage 856 of reducing, by a certain amount, receive        sensitivity threshold and possibly the effective clear channel        assessment threshold, if the receive sensitivity threshold is        still higher than the clear channel assessment threshold, upon a        lack of reception of at least one input frame that was expected        to be received by the wireless communication device; wherein the        certain amount varies over time.

FIG. 17 illustrates method 900 according to an embodiment of theinvention

Method 900 may include stage 910 of measuring, by a wirelesscommunication device, an attribute of transmissions of another wirelesscommunication device. Stage 910 may be followed by stage 920 ofdetermining the attribute of the collision avoidance scheme in responseto an attribute of the transmissions of the other wireless communicationdevice.

The wireless communication device may be an access point. The networkcommunication device and the other wireless communication device maybelong to different wireless networks. The network communication deviceand the other wireless communication device may belong to a samewireless network.

The attribute of the collision avoidance scheme may be a clear channelassessment threshold upper limit. The attribute of the collisionavoidance scheme may be at least one margin between an input signalsattribute and another attribute of the collision avoidance scheme.

Stage 920 may be followed by stage 930 of transmitting the attribute ofthe collision avoidance scheme to a further wireless communicationdevice.

FIG. 18 illustrates a wireless communication device 1000 according to anembodiment of the invention.

The wireless communication device may be any device capable ofwirelessly receiving and/or wirelessly transmitting signals and canexecute any of the methods illustrated in the specification. It may be astation, an access point, and the like.

The wireless communication device 1000 includes interface 1010,processor 1020, memory module 1030 and one or more wireless antennassuch as wireless antennas 1040. The interface 1010 may be a wirelessreceiver, a wireless transmitter, a combination thereof or a portionthereof. It may include, for example, at least a part of an analogand/or digital front end of a receiver, a transmitter or a combinationthereof.

The interface 1010 and/or the processor 1020 may include measurementelements for measuring and/or calculating attributes of received signals(input signals, transmissions).

According to an embodiment of the invention the interface 1010 isarranged to receive input signals and the processor 1020 is arranged tocalculate an input signal's attribute; and determine an attribute of acollision avoidance scheme in response to the input signal's attribute.The memory module may store instructions for executing any methodmentioned in the specification, input signals, results of processing ofthe processor 1020, signals to be outputted and the like.

According to an embodiment of the invention the interface 1010 isarranged to receive transmissions of another wireless communicationdevice and the processor 1020 is arranged to measure an attribute of thetransmissions of the other wireless communication device, and determinethe attribute of the collision avoidance scheme in response to anattribute of the transmissions of the other wireless communicationdevice.

According to an embodiment of the invention the interface 1010 isarranged to receive input signals and the processor 1020 is arranged tocalculate an input signal's attribute; and determine at least one out ofa sensitivity threshold and a clear channel assessment threshold;wherein a value of the clear channel assessment threshold is responsiveto a value of the sensitivity threshold.

The invention may also be implemented in a computer program for runningon a computer system, at least including code portions for performingsteps of a method according to the invention when run on a programmableapparatus, such as a computer system or enabling a programmableapparatus to perform functions of a device or system according to theinvention. The computer program may cause the storage system to allocatedisk drives to disk drive groups.

A computer program is a list of instructions such as a particularapplication program and/or an operating system. The computer program mayfor instance include one or more of: a subroutine, a function, aprocedure, an object method, an object implementation, an executableapplication, an applet, a servlet, a source code, an object code, ashared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer system.

The computer program may be stored internally on a non-transitorycomputer readable medium. All or some of the computer program may beprovided on computer readable media permanently, removably or remotelycoupled to an information processing system. The computer readable mediamay include, for example and without limitation, any number of thefollowing: magnetic storage media including disk and tape storage media;optical storage media such as compact disk media (e.g., CD-ROM, CD-R,etc.) and digital video disk storage media; nonvolatile memory storagemedia including semiconductor-based memory units such as FLASH memory,EEPROM, EPROM, ROM; ferromagnetic digital memories; MRAM; volatilestorage media including registers, buffers or caches, main memory, RAM,etc.

A computer process typically includes an executing (running) program orportion of a program, current program values and state information, andthe resources used by the operating system to manage the execution ofthe process. An operating system (OS) is the software that manages thesharing of the resources of a computer and provides programmers with aninterface used to access those resources. An operating system processessystem data and user input, and responds by allocating and managingtasks and internal system resources as a service to users and programsof the system.

The computer system may for instance include at least one processingunit, associated memory and a number of input/output (I/O) devices. Whenexecuting the computer program, the computer system processesinformation according to the computer program and produces resultantoutput information via I/O devices.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims.

Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under”and the like in the description and in the claims, if any, are used fordescriptive purposes and not necessarily for describing permanentrelative positions. It is understood that the terms so used areinterchangeable under appropriate circumstances such that theembodiments of the invention described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein.

The connections as discussed herein may be any type of connectionsuitable to transfer signals from or to the respective nodes, units ordevices, for example via intermediate devices. Accordingly, unlessimplied or stated otherwise, the connections may for example be directconnections or indirect connections. The connections may be illustratedor described in reference to being a single connection, a plurality ofconnections, unidirectional connections, or bidirectional connections.However, different embodiments may vary the implementation of theconnections. For example, separate unidirectional connections may beused rather than bidirectional connections and vice versa. Also,plurality of connections may be replaced with a single connection thattransfers multiple signals serially or in a time multiplexed manner.Likewise, single connections carrying multiple signals may be separatedout into various different connections carrying subsets of thesesignals. Therefore, many options exist for transferring signals.

Furthermore, the terms “assert” or “set” and “negate” (or “deassert” or“clear”) are used herein when referring to the rendering of a signal,status bit, or similar apparatus into its logically true or logicallyfalse state, respectively. If the logically true state is a logic levelone, the logically false state is a logic level zero. And if thelogically true state is a logic level zero, the logically false state isa logic level one.

Those skilled in the art will recognize that the boundaries betweenlogic blocks are merely illustrative and that alternative embodimentsmay merge logic blocks or circuit elements or impose an alternatedecomposition of functionality upon various logic blocks or circuitelements. Thus, it is to be understood that the architectures depictedherein are merely exemplary, and that in fact many other architecturesmay be implemented which achieve the same functionality.

Any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality may be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations merely illustrative. The multipleoperations may be combined into a single operation, a single operationmay be distributed in additional operations and operations may beexecuted at least partially overlapping in time. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

Also for example, in one embodiment, the illustrated examples may beimplemented as circuitry located on a single integrated circuit orwithin a same device. Alternatively, the examples may be implemented asany number of separate integrated circuits or separate devicesinterconnected with each other in a suitable manner.

Also for example, the examples, or portions thereof, may implemented assoft or code representations of physical circuitry or of logicalrepresentations convertible into physical circuitry, such as in ahardware description language of any appropriate type.

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code, such asmainframes, minicomputers, servers, workstations, personal computers,notepads, personal digital assistants, electronic games, automotive andother embedded systems, cell phones and various other wireless devices,commonly denoted in this application as ‘computer systems’.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the terms “a” or “an,” as used herein, are definedas one or more than one. Also, the use of introductory phrases such as“at least one” and “one or more” in the claims should not be construedto imply that the introduction of another claim element by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim element to inventions containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles. Unless statedotherwise, terms such as “first” and “second” are used to arbitrarilydistinguish between the elements such terms describe. Thus, these termsare not necessarily intended to indicate temporal or otherprioritization of such elements. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A method for determining an attribute of a carrier sense multipleaccess with collision avoidance (CSMA/CA) scheme, the method comprises:receiving, by an interface of a wireless communication device, an inputsignal; calculating, by a processor of the wireless communicationdevice, a strength of the input signal; and determining, by theprocessor, the attribute of the (CSMA/CA) scheme in response to thestrength of the input signal.
 2. The method according to claim 1 whereinthe input signal is a management frame that is transmitted by an accesspoint to which the wireless communication device is associated.
 3. Themethod according to claim 2 wherein the input signal is a beacon framethat is transmitted by an access point to which the wirelesscommunication device is associated.
 4. The method according to claim 3wherein the determining of the attribute of the (CSMA/CA) scheme isresponsive to the strength of the input signal when the strength of theinput signal does not exceed an upper limit.
 5. The method according toclaim 4 wherein the determining of the attribute of the (CSMA/CA) schemecomprises setting a clear channel assessment threshold in relation tothe strength of the input signal.
 6. The method according to claim 5comprising setting the clear channel assessment threshold to a levelthat is equal to the strength of the input signal minus a margin.
 7. Themethod of claim 6 comprising calculating the strength of the inputsignal by averaging strengths of input signals that were calculated atdifferent points in time within a time period.
 8. The method accordingto claim 7, comprising counting a number of successive missed beaconframes; defining a limit for a number of successive missed beaconframes; and reducing the attribute of the (CSMA/CA) scheme when thenumber of successive missed beacons exceeds the limit.
 9. The methodaccording to claim 1 wherein the attribute of the (CSMA/CA) scheme is areceive sensitivity threshold.
 10. The method according to claim 9comprising setting the receive sensitivity threshold to a level that isequal to the strength of the input signal minus a margin.
 11. The methodof claim 10 comprising calculating the strength of the input signal byaveraging strengths of input signal that were calculated at differentpoints in time within a time period.
 12. The method according to claim11, comprising counting a number of successive missed beacon frames;defining a limit for a number of successive missed beacon frames; andreducing the attribute of the (CSMA/CA) scheme when the number ofsuccessive missed beacons exceeds the limit.
 13. A wirelesscommunication device that comprises an interface and a processor;wherein the interface is arranged to receive an input signal; whereinthe processor is arranged to: calculate a strength of the input signal;and determine the attribute of the (CSMA/CA) scheme in response to thestrength of the input signal.
 14. The wireless communication deviceaccording to claim 13 comprising a transmitter, wherein the transmitteris arranged to transmit output signals according to the attribute of the(CSMA/CA) scheme.
 15. The wireless communication device according toclaim 14 wherein the input signal is a management frame that istransmitted by an access point to which the wireless communicationdevice is associated.
 16. The wireless communication device according toclaim 15 wherein the input signal is a beacon frame that is transmittedby an access point to which the wireless communication device isassociated.
 17. The wireless communication device according to claim 16wherein the processor is configured to determine the attribute of the(CSMA/CA) scheme in response to the strength of the input signal whenthe strength of the input signal does not exceed an upper limit.
 18. Thewireless communication device according to claim 17 wherein theprocessor is configured to determine the attribute of the (CSMA/CA)scheme by setting a clear channel assessment threshold in relation tothe strength of the input signal.
 19. The wireless communication deviceaccording to claim 18 wherein the processor is configured to set theclear channel assessment threshold to a level that is equal to thestrength of the input signal minus a margin.
 20. The wirelesscommunication device of claim 19 wherein the processor is configured tocalculate the strength of the input signal by averaging strengths ofinput signals that were calculated at different points in time within atime period.
 21. The wireless communication device according to claim20, wherein the processor is configured to count a number of successivemissed beacon frames; define a limit for a number of successive missedbeacon frames; and reduce the attribute of the (CSMA/CA) scheme when thenumber of successive missed beacons exceeds the limit.
 22. The wirelesscommunication device according to claim 13 wherein the attribute of the(CSMA/CA) scheme is a receive sensitivity threshold.
 23. The wirelesscommunication device according to claim 22 wherein the processor isconfigured to set the receive sensitivity threshold to a level that isequal to the strength of the input signal minus a margin.
 24. Thewireless communication device according to claim 23 wherein theprocessor is configured to calculate the strength of the input signal byaveraging strengths of input signal that were calculated at differentpoints in time within a time period.
 25. The wireless communicationdevice according to claim 24, wherein the processor is configured tocount a number of successive missed beacon frames; define a limit for anumber of successive missed beacon frames; and reduce the attribute ofthe (CSMA/CA) scheme when the number of successive missed beaconsexceeds the limit.
 26. A non-transitory computer readable medium thatstores instructions that once executed cause a wireless communicationdevice to computer to: receive an input signal; calculate a strength ofthe input signal; and determine the attribute of the (CSMA/CA) scheme inresponse to the strength of the input signal.